Americans quaff nearly 10 billion gallons of bottled water each year, in large part because they assume, wrongly, that it’s healthier and safer than tap water. Somewhat surprisingly, the data has suggested, underserved black and Latino families tend to spend more money than whites do on bottled water, and provide it exclusively for their kids.

While previous research has shown that minorities use bottled water more often than whites, the question has always been, why? A new study in the Archives of Pediatric Adolescent Medicine aimed to find out, by surveying 632 parents, 32% of whom were Latino, 33% African American, and 35% white.

The study’s authors, from the department of pediatrics at the Medical College of Wisconsin, report that African American and Latino parents were three times more likely to give their children bottled water exclusively, compared with white parents. When questioned about their habits, minority parents reported that that they thought bottled water was cleaner, safer, healthier, more convenient and better tasting than tap.

In fact, the study author’s note, bottled water may be prone to bacterial contamination. A National Resources Defense Council investigation found that 17% of bottled waters had bacterial loads that were considered unsafe; 22% were tainted with enough chemicals, including arsenic, that they wouldn’t pass the strictest state standards.

What’s more, data have associated bottled water with diarrheal illness in kids: a 2010 study found that 45% of children who sought treatment for severe diarrhea drank only bottled water. And kids who use bottled water exclusively in place of tap may not get enough exposure to fluoride, which can affect their oral health. (It’s worth noting, too, that about one-quarter of all bottled waters are actually just tap water, repackaged — regardless of the pure mountain spring on the label.)

Overall, bottled water use was high, the current survey found, with 45% of parents saying their kids drank primarily or exclusively from bottled sources (broken down by ethnicity, more than 20% of Latino and black parents used only bottled water, compared with 10% of white parents). Factors like household income or previous residence outside the U.S. — where in many places bottled water may actually be healthier and cleaner than municipal sources — weren’t associated with bottled water consumption.

Indeed researchers found that families with lower incomes were more likely to buy bottled water: white families reported spending an average 0.4% (or about $12 a month) of their household income on bottled water, while African American and Latino families spent an average 1% (or $20 a month) of their incomes. Further, 12% of African American respondents and 14% of Latino respondents reported having to sacrifice other goods in order to afford their bottled water habit.

“The disproportionate use of bottled water by poor and minority families may contribute to health disparities,” write the authors. “Despite these perceptions about the safety and health effect of bottled water, there is little if any objective evidence that in most circumstances there is any actual health benefit of bottled water over tap water in the United States.”

Given the high cost and health consequences of consuming exclusively bottled water, the researchers hope their efforts will lead to public education campaigns about water from the tap: it’s free, it’s healthy and it usually even tastes good.